In the papermaking art, wet strength agents like epichlorohydrin-based resins, for example polyaminoamide epichlorohydrin resins have been used for a long time to enhance the strength of paper. Such resins are disclosed in U.S. Pat. Nos. 3,700,623 and 3,772,076. The wet strength of a paper relates to its ability to maintain physical integrity and to resist tearing, bursting, and shredding under use, especially under wet conditions. A further important property of wet strengthened paper is the softness, especially for tissue paper or the like. The softness can be described as the tactile sensation perceived when holding or rubbing a paper across the skin. U.S. Pat. No. 5,200,036 discloses a wet strength agent which provides paper with enhanced wet strength. A cationic polyaminoamide epichlorohydrin resin is modified by introduction of a polymerisable unsaturated hydrocarbon moiety thus providing it with ethylenically unsaturated side-chain substituents. The resin is then added to latex-forming monomers whereby co-polymerisation occurs forming bonds between unsaturated polymerisable hydrocarbon moieties of the resin and the latex-forming monomers. The reaction may be assisted by addition of an emulsifier to obtain a desirable suspension of the formed latex panicles. Resins of the above-mentioned types are also used as emulsifiers. Usually, the resins are not effective enough when used as a sole emulsifier and these are thus used in combination with an additional compound.
U.S. Pat. No. 5,314,721 discloses a process for preparation of vinyl polymer dispersions comprising resin based on a cationic polyaminoamide whose terminal groups have been substituted with long-chain aliphatic hydrocarbon radicals which have at least 7 carbon atoms and are derived from monocarboxylic acids. The product obtained is used as a sizing agent.
U.S. Pat. No. 4,416,729 discloses a method for preparing wet strength additives comprising the steps of contacting a linear polyamidoamine with an α,β-ethylenically unsaturated carboxylic compound to form a substituted polyamidoamine, contacting the substituted polyamidoamine with a polyamine to form a branched polyamidoamine bearing a pendant amine moiety, and contacting the branched polyamidoamine with an epihalohydrin to form pendant curable ammonium moieties on the branched polyamidoamine. U.S. Pat. No. 4,416,729 does not disclose use of the prepared wet strength additives for production of tissue paper.
Although the above epichlorohydrin-based resins in some applications show adequate wet strength and emulsifying properties, it would be desirable to be able to provide further and improved wet strength agents for paper and methods for providing such agents. It would also be desirable to be able to provide wet strength resins and agents exhibiting improved softness properties. Further, it would be desirable to be able to provide further resins having improved emulsifying properties.